Polyester imide wire enamels

ABSTRACT

Superior wire enamels comprise polyester imides prepared in the presence of a monophenyl ether of a glycol having a free secondary hydroxyl group and dissolved in a solvent comprising predominantly a polar oxygenated compound selected from a monoether or monoester of an alkylene, or polyalkylene, glycol. Electrical conductors coated with such enamels are also disclosed.

This invention relates to polyester imide wire enamels and to electricalconductors coated therewith. More particularly, it is concerned withester imides prepared in the presence of a monophenyl ether of a glycolhaving a secondary hydroxyl group and dissolved in a non-phenolicsolvent which is predominantly polar and oxygenated.

BACKGROUND OF THE INVENTION

British Pat. No. 973,377 discloses a family of ester imide resins madeby reacting together at least one polybasic acid or a functionalderivative thereof, and at least one polyhydric alcohol or functionalderivative thereof, at least one of the reactants having at least onefive-membered imide ring between the functional groups of the molecule.It further discloses that the reactants can be heated in a commercialcresol mixture, then further diluted in a mixture of naphtha and cresoland used as an enamel for coating copper wire to produce a hard,thermally resistant insulation therefor. U.S. Pat. No. 3,426,098describes ester imide resins in which all or part of the polyhydricalcohol comprises tris(2-hydroxyethyl) isocyanurate. U.S. Pat. No.3,382,203 describes polyester wire coating enamels based on mixed esterscontaining aromatic polycarboxylic acid radicals and radicals of di-and/or polyhydric alcohols, and specifically contemplates the inclusionof imide containing units. A preference is stated for cresol as asolvent. U.S. 3,274,159 describes polyester polyimides of trimelliticanhydride in which a glycol reactant is stated to be present in excessof stoichiometric proportions when no solvent is employed in thepolymerization reaction. Such polyester polyimides are stated to beuseful as outdoor wire insulation material. U.S. Pat. No. 3,141,859acknowledges that certain esters and ethers of ethylene glycol andpolyethylene glycol can be used in the preparation of alkyd resins tomake wire enamels, but it is not disclosed if such compounds are mono-or di- ethers and esters, and, in any event, the statement is made that"completely satisfactory wire enamels have not been obtained by such aprocess." The disclosures of the foregoing patents are incorporatedherein by reference.

Keating, U.S. Pat. Nos. 4,119,605, 4,119,608; and 4,119,758,incorporated herein by reference, discloses polyester-imide resins whichare soluble in non-phenolic solvents by incorporating a monoether of adiethylene glycol or a triethylene glycol into the resin. It is statedtherein that the use of the monoether of a glycol as a reactant whichserves as a monofunctional alcohol serves to control the molecularweight and solubility of the polymer and permits the manufacture of wireenamels which contain relatively non-toxic solvents in place of phenolsand also permits the attainment of enamels having economical high solidscontents. The reactive glycol dealt with by the abovementioned Keatingpatents is an ether alcohol which either (a) has the formula RO(C_(n)H_(2n) O)_(x) H where R is an alkyl group of 1 to 6 carbon atoms orphenyl, n is 2 or 3 and x is 2 or 3 or (b) is the monophenyl ether ofethylene glycol.

Enamels prepared with such reactive monohydric alcohols are not entirelysatisfactory in comparison with conventional polyester imides because,while reacting the ether alcohol into the resin lowers its molecularweight and improves solubility, it also tends to reduce ultimatephysical properties precisely because the molecular weight has beenlowered.

It has now been discovered that if polyester imide resins are preparedin the presence of a monophenyl ether of a branched aliphatic glycolhaving at least 3 carbon atoms in the aliphatic chain and in which themonohydric alcohol group is a secondary alcohol group, e.g.,1-phenoxy-2-propanol, then there is little tendency for the glycol etherto react into the resin, and the molecular weight is higher than itwould be if a glycol ether of the type described in the Keating patentsis employed. The result is that a superior wire enamel can be made bydissolving such higher molecular weight resins in a solvent comprisingpredominantly the same, or different, polar organic monoethers ormonoesters of alkylene glycols or polyalkylene glycols. The presentenamels are clear solutions, even without chemically binding in theglycol ether. They thus eliminate the need for cresylic acid solvent andtherefore provide excellent results without any toxic effluents.

DESCRIPTION OF THE INVENTION

According to the present invention, there are provided electrical wireenamels comprising:

(a) a polyester imide obtained by heating ingredients consistingessentially of

(i) an aromatic diamine;

(ii) an aromatic carboxylic anhydride containing at least one additionalcarboxylic group;

(iii) terephthalic acid or a reactive derivative thereof;

(iv) a polyhydric alcohol having at least three hydroxyl groups;

(v) an alkylene glycol; and

(vi) 1-phenoxy-2-propanol until reaction therebetween is substantiallycomplete; and

(b) a solvent therefor comprising predominantly

(i) an alkylene glycol monoether or monoester.

(ii) a polyalkylene glycol monoether or monoester or

(iii) a mixture of (i) and (ii).

Among the preferred features of the present invention are electricalwire enamels as defined above which also include an alkyl titanate.

Also contemplated by the present invention are electrical conductorsprovided with a continuous coating of the new wire enamels, and cured atelevated temperatures.

With respect to components a(i)-a(v) inclusive these are conventionaland well known to those skilled in this art by reason of the teachings,for example, in the above-mentioned U.K. Patent Specification No.973,377, and U.S. Pat. No. 3,426,098.

By way of illustration, aromatic diamine component (a)(i) can comprisebenzidine, methylene dianiline, oxydianiline, diaminodiphenyl ketone,-sulfone, -sulfoxide, phenylene diamine, tolylene diamine, xylenediamine, and the like. Preferably, component (a)(i) will compriseoxydianiline or methylenedianiline, and especially preferably,methylenedianiline.

Illustratively, the aromatic carboxylic anhydride containing at leastone additional carboxylic group component (a) (ii) can comprisepyromellitic anhydride, trimellitic anhydride, naphthalenetetracarboxylic dianhydride, benzophenone-2,3,2',3'-tetracarboxylicdianhydride, and the like. The preferred components (a)(ii) arepyromellitic anhydride or trimellitic anhydride and especiallytrimellitic anhydride.

Typically, terephthalic acid or a di(lower)alkyl ester (C₁ -C₆) or otherreactive derivative, e.g., amide, acyl halide, etc. will be used ascomponent (a)(iii). A minor amount of the terephthalic acid can bereplaced with another dicarboxylic acid or derivative, e.g., isophthalicacid, benzophenone dicarboxylic acid, adipic acid, etc. Preferablycomponent (a)(iii) will comprise dimethyl terephthalate or terephthalicacid, and especially preferably, terephthalic acid.

As optional polyester forming ingredients (a)(iv) there may be employeda polyhydric alcohol having at least three hydroxyl groups, there can beused glycerine, pentaerythritol, 1,1,1-trimethylolpropane, sorbitol,mannitol, dipentaerythritol, tris(2-hydroxyethyl)isocyanurate (THEIC),and the like. Preferably as component (a)(iv) there will be usedglycerine or tris(2-hydroxyethyl) isocyanurate, preferably the latter.

Illustratively, the alkylene glycol component (a)(v) will compriseethylene glycol, 1,4-butanediol, trimethylene glycol, propylene glycol,1,5-pentanediol, 1,4-cyclohexane dimethanol and the like. Preferably thealkylene glycol will be ethylene glycol.

The 1-phenoxy-2-propanol component (vi) can be made in known ways, andit is also available commercially. It has a molecular weight of 152.2,and a freeze point of about 11.4° C. Its boiling point at 760 mm Hg. is242.7° C. It is sold by Dow Chemical Co., Midland, Michigan 48640,U.S.A. under the tradename DOWANOL PPh.

The polar oxygenated solvent (b) having at least one active hydroxylgroup will be selected from (i) an alkylene glycol monoether ormonoester, such as ethylene glycol monomethyl ether, or monoester, suchas ethylene glycol monomethyl ether, ethylene glycol mono-n-butyl ether,ethylene glycol monohexyl ether, ethylene glycol monoacetate, ethyleneglycol monohexanoate, propylene glycol monomethyl ether, propyleneglycol monoacetate, 1,4-butylene glycol mono-n-butyl ether, 1,6-hexyleneglycol monomethyl ether, and the like, preferably ethylene glycolmonomethyl ether and ethylene glycol monophenyl ether, and for (ii) apolyalkylene glycol monoether or monoester, such as diethylene glycolmonoethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycolmonoacetate, diethylene glycol monophenyl ether, triethylene glycolmonomethyl ether, triethylene glycol monoacetate, etc. Preferably, therewill be used diethylene glycol monomethyl or diethylene glycol monobutylether.

Suitable alkyl titanates include tetraisopropyl titanate, tetramethyltitanate, tetrabutyl titanate, tetrahexyltitanate,bis(acetoacetonyl)diisopropyl titanate and the like. Tetraisopropyltitanate is preferred.

In making the polyester imide there should normally be an excess ofalcohol groups over carboxyl groups in accordance with conventionalpractice. The preferred ratios of ingredients, and of ester groups toimide groups, are entirely conventional, see the patents cited above,and the especially preferred ratios of ingredients will be exemplifiedin detail hereinafter. The manner of making the polyester imide islikewise conventional. Either the polyester or the polyimide componentscan be made first, and subsequently reacted at elevated temperatures, orall of the ingredients can be added at the beginning and reacted.Preferably, the ingredients are all added to a suitable reactor andheated to 200° to 250° C. until no more water distills off. Thisindicates substantial completion of the reaction. This may take severalhours. Then the mixture is cooled somewhat, e.g., to 150° to 190° C. andthen glycol ether or ester is added as solvent, preferably with a minorproportion of a hydrocarbon diluent, e.g., an aromatic naphtha, such asSolvesso 100 or toluene, dodecane, and the like.

The wire enamels thus made are applied to an electrical conductor, e.g.,copper, silver or stainless steel wire, in conventional fashion.Illustratively, wire speeds of 15 to 65 feet/min. can be used with wiretower temperatures of 250° to 900° F. The build up of coating on thewire can be increased by repetitive passes through the enamel. Thecoatings produced from the present enamels have excellent smoothness,flex resistance, continuity, solvent resistance, heat aging, dissipationfactors, cut through resistance, heat shock, abrasion resistance anddielectric strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention. They are notintended to limit the scope of the claims in any manner whatsoever.

EXAMPLE 1

A wire enamel is made by charging a suitably sized flask with thefollowing reactants

    ______________________________________                                                             Gms                                                      ______________________________________                                        Tris(2-hydroxyethyl)isocyanurate                                                                     1066.9                                                 Trimellitic anhydride  746.2                                                  Methylenedianiline     387.5                                                  Ethylene glycol        278.5                                                  Terephthalic acid      757.3                                                  Tetraisopropyltitanate 6.02                                                   1-Phenoxy-2-propanol   574.9                                                  ______________________________________                                    

The contents are heated slowly with the evolution of water to a maximumtemperature of 230° C. until no more water is given off. The contentsare allowed to cool to 200° C. and poured into a metal tray to solidify.

Resin, 700 g., is dissolved in 386 g. of the monomethyl ether ofdiethylene glycol and 141 g. of hydrocarbon solvent (Solvesso-100). Tothis solution is added 36.9 g. of phenolic resin in 40 g. of diethyleneglycol monomethyl ether and 14.9 g. of tetraisopropyltitanate in 30 g.of diethylene glycol monomethyl ether and 10 g. of Solvesso-100. Theclear amber solution has a viscosity of 1290 centistokes (cs) at 25° C.and a solids content of 46.44%.

When applied in a 15 foot vertical tower at 900° F. on 18 AWG copper in7 passes, a coated wire having the following properties are obtained at50'/min.

Cut Thru, °C.--395

For comparison purposes a wire enamel of this type is made substitutinga reactive monophenyl ether of ethylene glycol and dimethylterephthalate for terephthalic acid.

COMPARATIVE EXAMPLE 1A

The following materials are reacted in a suitably-sized flask:

    ______________________________________                                                              GMS                                                     ______________________________________                                        tris(2-hydroxyethyl)isocyanurate                                                                      301                                                   Trimellitic anhydride   221                                                   Methylenedianiline      114                                                   Ethylene glycol          93                                                   Dimethyl terephthalate  257                                                   Tetraisopropyltitanate  0.34                                                  Ethylene glycol monophenyl ether                                                                      335                                                   ______________________________________                                    

The contents are heated slowly with the evolution of water and methanolcollected in a Dean Stark trap. The contents are heated to a maximum of240° C. until the theoretical amount of water is collected. To the clearsolution is added, at 180° C., 487 gms. of monomethyl ether ofdiethylene glycol. The contents are allowed to cool to 150° C. then 205gms. Solvesso 100 naphtha solvent is added. The clear amber solution hasa viscosity of 470 cs at 25° C. and a solids content of 50.8%.

When applied on a 15 foot vertical tower at 900° F. on 18 AWG copper in7 passes, a coated wire having the following properties is obtained at40'/min.:

Cut Thru, °C.--360

EXAMPLE 2

A suitably sized flask is charged with the following:

    ______________________________________                                                              GMS                                                     ______________________________________                                        Tris-(2-hydroxyethyl)isocyanurate                                                                     955.5                                                 Trimellitic anhydride   927.6                                                 Methylenedianiline      522.1                                                 Ethylene glycol         238.4                                                 Terephthalic acid       583.3                                                 Tetraisopropyltitanate   6.0                                                  1-Phenoxy-2-propanol    584.0                                                 ______________________________________                                    

The contents are heated slowly with the evolution of water to a maximumtemperature of 225° C. until no more water is given up. The contents areallowed to cool to 200° C. and poured into a metal tray to solidify.

Resin, 700 g., is dissolved in 484 g. of the monomethylene glycol and161 g. of Solvesso-100. To this solution is added 11.6 g. oftetraisopropyltitanate in 30 g. of diethylene glycol monomethyl etherand 10 g. of Solvesso-100. The clear amber solution has a viscosity of978 cps. at 25° C. and a solids content of 43.8%.

When applied in a 15 foot vertical tower at 900° F. on 18 SWG copper in7 passes, a coated wire having the following properties is obtained at50'/min.

Cut Thru, °C.--362

Heat Shock 0% 30 min. at 200° C.--2X

For comparison purposes a wire enamel of this type is made substitutinga reactive monobutyl ether of diethylene glycol for the substantiallynon-reactive 1-phenoxy-2-propanol.

COMPARATIVE EXAMPLE 2A

A flask is charged with the following

    ______________________________________                                                              GMS                                                     ______________________________________                                        Tris(2-hydroxyethyl)isocyanurate                                                                      301.2                                                 Trimellitic anhydride   221.6                                                 Methylenedianiline      114.2                                                 Ethylene glycol         93                                                    Terephthalic acid       220.5                                                 Tetraisopropyltitanate  .34                                                   Diethylene glycol monobutyl ether                                                                     210.5                                                 ______________________________________                                    

The contents are heated slowly with the evolution of water to a maximumtemperature of 225° C. until no more water is given off. The contentsare allowed to cool to 180° C. at which time 632 gms of monomethyl etherof diethylene glycol is added along with 211 gms of Solvesso 100. Thecontents are filtered. Final solids are 45% with a viscosity of 550 cpsat 25° C.

The enamel is run at 50'/min. on a wire tower at 900° F. using 7 passeson 18 AWG copper wire. A coated wire having the following properties isobtained:

Flex 25%--1X

Cut Thru, °C.--249

Heat Shock 0%-30°'-200° C.--3X

In all cases it is seen that coated wires having improved properties,especially cut through and heat shock, are obtained when the polyesterimide is prepared in the presence of substantially non-reactive1-phenoxy-2-propanol.

It is obviously possible to make many variations in the presentinvention in light of the above, detailed description. For example, thealkyl titanate can be omitted. A polyisocyanate, 1 to 25% based onresin, can be added, phenol-formaldehyde resin can be omitted or it canbe substituted with a melamine-formaldehyde resin. Metal driers can alsobe added, e.g., 0.2 to 1.0% based on total solids, of zinc octoate,cadmium linoleate, calcium octoate, and the like. Instead of themonomethyl ether or diethylene glycol used as solvent, there can be usedthe monobutyl ether of diethylene glycol. The following monoesteralcohols can be used: ethylene glycol monoacetate and diethylene glycolmonoacetate. All such obvious variations are within the full intendedscope of the appended claims.

What is claimed is:
 1. An electrical wire enamel comprising:(a) apolyester imide obtained by heating ingredients consisting essentiallyof(i) an aromatic diamine; (ii) an aromatic carboxylic anhydridecontaining at least one additional carboxylic group; (iii) terephthalicacid or a di(C₁ -C₆) alkyl ester, amide or acyl halide thereof; (iv) apolyhydric alcohol having at least three hydroxyl groups; (v) analkylene glycol; and (vi) an effective amount of 1-phenoxy-2-propanol toreduce molecular weight abatement until reaction therebetween issubstantially complete; and (b) a solvent therein comprisingpredominantly(i) an alkylene glycol monoether or monoester, (ii) apolyalkylene glycol monoether or monoester or (iii) a mixture of (i) and(ii).
 2. An electrical wire enamel as defined in claim 1 which alsoincludes an alkyl titanate.
 3. An electrical wire enamel comprising(a) apolyester imide obtained by heating ingredients consisting essentiallyof(i) methylene dianiline: (ii) trimellitic anhydride; (iii)terephthalic acid; (iv) tris(2-hydroxyethyl)isocyanurate; (v) ethyleneglycol; and (vi) an effective amount of 1-phenoxy-2-propanol to reducemolecular abatement until reaction therebetween is substantiallycomplete; and (b) a solvent therefor comprising predominantly (i)diethylene glycol mono-n-butyl ether, diethylene glycol monomethyl etheror a mixture thereof.
 4. An electrical wire enamel as defined in claim 3which also includes tetraisopropyl titanate.
 5. An electrical wireenamel comprising(a) a polyester imide obtained by heating ingredientsconsisting essentially of(i) an aromatic diamine selected from the groupconsisting of benzidine, methylene dianiline, oxydianiline,diaminodiphenyl ketone, diaminodiphenyl sulfone, diaminodiphenylsulfoxide, phenylene diamine, tolylene diamine and xylene diamine; (ii)an aromatic carboxylic anhydride selected from the group consisting ofpyromellitic anhydride, trimellitic anhydride, naphthalenetetracarboxylic dianhydride and benzophenone-2,3,2',3'-tetracarboxylicdianhydride; (iii) terephthalic acid or a di alkyl ester, amide or acylhalide thereof; (iv) a polyhydric alcohol selected from the groupconsisting of glycerine, pentaerythritol, 1,1,1-trimethylolpropane,sorbitol, mannitol, dipentaerythritol and tris(2-hydroxymethyl)isocyanurate; (v) an alkylene glycol selected from the group consistingof ethylene glycol, 1,4-butanediol, trimethylene glycol, propyleneglycol, 1,5-pentanediol and 1,4-cyclohexane dimethanol; and (vi) aneffective amount of 1-phenoxy-2-propanol to reduce molecular weightabatement until reaction therebetween is substantially complete; and (b)a solvent therein comprising predominantly(i) an alkylene glycolmonoether or monoester; (ii) a polyalkylene glycol monoether ormonoester, or (iii) a mixture of (i) and (ii).
 6. An electrical wireenamel as defined in claim 5 which also includes an alkyl titanate.